var DustObj = function  () {
	this.x = [];
	this.y = [];
	this.amp = [];
	this.NO = [];
	this.alpha = 0;
	this.num = 30;
}
DustObj.prototype.init = function() {
	for (var i = this.num - 1; i >= 0; i--) {
		this.x[i] = Math.random() * can_w;
		this.y[i] = Math.random() * can_h;
		this.amp[i] = Math.random() * 15 + 10;
		this.NO[i] = Math.floor( Math.random() * 7);

	};
};
DustObj.prototype.draw = function() {
	this.alpha += deltaTime * 0.0015;
	var l = Math.sin(this.alpha);
	for (var i = this.num - 1; i >= 0; i--) {
		var no = this.NO[i];
		ctx2.drawImage( dustPic[no], this.x[i] + this.amp[i] * l, this.y[i]);

	};
};